1. Field of the Invention
The invention relates to an arrangement for fastening a rotor of a side channel compressor to a shaft.
2. Description of the Prior Art
In side channel compressors, the spacing between the rotor and the housing is required to be very small. This requirement stems from the desire, on the one hand, to obtain minimum gap losses and, on the other hand, to obtain cost-effective production. The effort to achieve such small spacings or gaps is particularly great in the case of multistage side channel compressors, since with these compressors the sum of ordinary manufacturing tolerances can easily exceed the permissible position deviation of the rotors.
To avoid excessive gaps between the rotor and housing of side channel compressors, it has been suggested that the rotor be fastened on its respective shaft by means of a hardening plastic. With this kind of fastening, the rotor can first be brought into an optimum position relative to the housing walls of the compressor with little difficulty or effort, and thereafter, it can be fastened to the shaft by means of a hardening plastic which is introduced in the liquid condition between the rotor hub and the shaft.
The drawings of the German Auslegeschrift No. 10 43 540 show the use of a hardening plastic to fasten a permanent magnet forming the rotor of a motor on a shaft. In this known arrangement, a sleeve is provided between the permanent magnet and the shaft and the diameter of the sleeve is made larger than that of the shaft to ensure that a sufficient amount of hardening plastic can be inserted therebetween. Due to the difference in diameters of the sleeve and shaft, however, there is now a danger that the permanent magnet will be fastened on the shaft eccentrically. While this eccentricity may not be important in rotors of small d-c machines, as is the case of this known arrangement, it cannot be tolerated in a rotor of a side channel compressor which rotates at several thousand r.p.m. This known fastening arrangement is thus not directly applicable to the fastening of the rotor of a side channel compressor to a shaft.
Eccentricity between the rotor of a side channel compressor and its shaft can be avoided in a relatively simple manner by arranging the rotor on the shaft with a correspondingly tight seat. If a hardening resin is now introduced between the shaft and rotor, as per the known fastening technique, the tight seat provided results in only a correspondingly thin layer of plastic between the rotor and shaft. It has been found, however, that particularly if the rotor and the shaft are formed of materials with different coefficients of expansion, such a thin layer is torn from the rotor and shaft if the latter are heated up. The layer, therefore, no longer fills the gap which develops between the rotor and shaft due to their different amounts of expansion and there is then no longer a positive, force-transmitting connection between the shaft and rotor.
It is, therefore, an object of the present invention to provide an arrangement for fastening a rotor of a side channel compressor to a shaft in such a manner as to avoid eccentricity of the rotor relative to the shaft, while still realizing a sufficiently strong connection therebetween.